Light controlling method and means



Aug. 8, 1933. 'A wHlTAK 1,921,852

LIGHT CONTROLLING METHOD AND MEANS Filed Oct. 25, 1928 rig O [Z 2 0mm 5 f% :8 IO 9 llunmll ATI'OIPA/EVS Patented Aug.8, 1933 I 1 1,921,852

MEANS Alfred Whitaker, West Drayton, England, as-

signor, by mesneassignments, to Radio Corporation of America, New York, N. Y., a Corporation of Delaware Application October 25, 1928,"-Serial No. 315,047, v and in Great Britain October 29, 1927 7 ll. Claims. (Cl. 179-1003) The present invention relates to means for action and, although some kinds of celluloid have controlling the intensity of a beam of light thissmall lag, other kinds have not. One end in accordance with variations 'in mechanical of this body 5 is fixed at (Sand the other end force produced by sounds or other mechanical" is attached to a coil 7 situated in an annular 5 oscillations. v I air gap 8 between two magnetic poles 9 and 10. 60

It is known that certain transparent bodies The currents to be transformed into changes'of V which are isotropic when they are unstressed, light intensity are passed through this coil '7 nevertheless. become birefringent-when they are and give rise to alternate tensions and compresstressedJ This effect is termed a photo-elastic sions in the body 5. The body 5 may, as shown,

10 effect. be so shaped that the point of maximum stress 65 According to the present invention, the in- .1 in the p o h beam of light- A Side tensity of a beam of polarized light is controlled view of the body 5 is given in Fig. 2. It will in accordance with sound, or other mechanical be clear, that if in the position of rest, the oscillations, by applying corresponding oscillaprisms are 50 ar d t no light Passes,

tory stresses to a body whichin the unstressed 'upon s es the op c body between the 70 condition is isotropic, the beam, of light being prisms, the resulting birefringence will produce passed through said body. The invention is to what is in many Way equiva t to a ro at on be understood to cover the use of bodies which of the plane of polarization p od by e are anisotropic provided that they are used in fi p i consequently some light will p such combinations that the effects exhibited are tht'ollgh thesecondprismy, o ev be 75 equivalent to those shown by an isotropic body. advantageous to arrange h p i m i uch a An initial stress may, if desired, b applied to manner that complete extinction of the light the body, in which case the body in'its normal o takes place at n ex reme value of either working conditionwill, of course, not be isocompressive or tensile stress. The light between tropic. The initial stress may be a steady o the two prisms may be allowed to remain in, a 80 an oscillatory stress, and if the stress is oscil- "p a l l be m o it m y be b o g t to a focus latory, it may have ,a frequency equal to the fat the body and again converted into a parallel natural frequency of the body or to a harmonic b b o p s n h the Second prism. thereof, The light beam, after modulation, passes The invention will be described, as) p1i d, through an optical system indicated by 11 and 85 to the conversion of electrical oscillations corthrough aslit 12 n to a v ng filln 13 where responding to sounds into corresponding changes a record of the changes in stress applied to the in theintensity or" a beam of light, with referbody 5 is made upon the film in the form of once to the accompanying drawing in which transverse lines oi varying degree of blacken- Fig. 1 is a diagrammatic view in front sec- 11 tional elevation of an arrangement in accord- In t form of the invention illustrated in ance with the invention. v 3, parts which correspond to those already de- Fig. 2 is a View. in side elevation of a detail scribed in Fig. 1 are given the same reference ofFig. 1. h V I numbers. e 40 Fig. 3 is a par'tsectional viewof another ar- In this arrangem the light beam is passed rangement according to the invention. 1 o g tW transparent isotropic odi s 4 and;

. Referring to Fig. 1, a beam of light, which 15 which may beof glass. The body 14 has a may, for example,. be monochromatic, from the convex surface," which contacts at a point, or source 1 is formed by suitable optical means 2 along a line, withthe fiat surface of the body 45 into a parallel beam and is passed through two '15- he light ea is caused t P s through V I polarizing prisms 3 and 4, and in the path of the point or line of contact, and the varying A the light between the prisms Band 4 isarstresses produced at this pointer line'of conranged a body 5 which in an unstressed conditact wheniacoustic or the like currents are tion is isotropioand which is atleast partially passed through the coil 'I produce, as before;

W 5 transparent. Suitablebodies-are, for example, effective rotation of the plane of polarization glass, celluloid or the like material. These subof, the light beam. V stances have the advantage of. producing a .An initialcompressive stress is applied in any relatively large effect per unit mechanical stress. suitable manner to'the bodies 14 and 15. Means They are also cheap and easily. worked: The ,for. producing such a stress are indicated dia- 55 material selected should have asmall' lag in its grammatically; by the springs] 16. The initial stress must be such that the applied currents at no time reduce the stress quite to zero.

In one form of the arrangement illustrated in Fig. 3, the body 14 is of part cylindrical shape and therefore there is line contact between the bodies 14. and 15. By using a suitable optical system 11, this line of contact can.

be brought to a sharp focus upon the surface of the film l3 and the slit 12 may be dispensed with. When currents of varying magnitude and sign are applied to the coil '7, the fine line of light remains of substantially the same width but the intensity of its illumination varies.

One advantage of the present method of light modulation is that the parts which are set in mechanical vibration by the currents passed through the coil 7 may be made relatively heavy without impairing the performance at higher frequencies since the operation of the apparatus is dependent only upon changes of stress and the amplitude of vibration may be made exceedingly small.

In another form of the invention, which is not illustrated, the electrical oscillations may be applied either directly or, after their voltage had been stepped up, to a piezo-electric crystal, the stresses set up thereby being transmitted to the isotropic body. In this form of the invention, a battery of piezo-electric crystals is preferably used, a number of crystals being arranged one above the other with conducting material between them, conducting material being also placed at both ends of the pile, and alternate conducting layers being connected together. It will be clear that diiferences of potential applied to the two sets of conductors will cause changes in shape of the battery of crystals and if these are attached to the isotropic body they will produce changes in stress therein.

In a further modification, two crystals of an anisotropic material, such as quartz, may be used, one of the crystals producing a right handed rotation and the other producing a left handed rotation of the plane of polarization,

the two rotations being equal and opposite. The combination is therefore in effect an isotropic body.

Although the invention has been described as applied to the conversion of electrical oscillations into changes of light intensity, it will be clear that it is not confined to this. For example, mechanical oscillations may be applied directly to the isotropic body.

In all cases, it will be understood that the isotropic body may be initially stressed and oscillatory stresses may be superimposed upon the unidirectional stress. The steady unidirectional stress may be either a tensile or a compressive stress.

It will be understood that the beam of light passed through the isotropic body may be wholly or partially plane polarized, or it may even be wholly or partially elliptically polarized.

The mechanical oscillations applied to the body may, in some cases, be in the form of high frequency oscillations modulated with acoustic or other relatively low frequency mechanical oscillations.

I claim:

1. A method of controlling the intensity of a beam of polarized light in accordance with sound vibrations which consists in applying an initial mechanical stress to a body that is isotropic in the unstressed condition and birefringent when stressed, passing a beam of polarized light through said body, and applying to said body additional mechanical stresses corresponding to said sound vibrations.

2. A method of controlling the intensity of a beam of polarized light in accordance with sound vibrations which consists in applying an intial mechanical stress to a body that is isotropic in the unstressed condition and birefringent when stressed, passing a beam of polarized light through said body, applying to said body an additional high frequency mechanical stress, and modulating said high frequency stress in accordance with said sound vibrations.

3. A method of controlling the intensity of a beam of polarized light in accordance with sound vibrations which consists in applying an initial mechanical stress to a body that is isotropic in the unstressed condition and birefringent when stressed, passing a beam of polarized light through said body, generating an electric current corresponding to said sound vibrations, and employing said current to apply additional mechanical stresses to said body.

4. A method of controlling the intensity of a beam of polarized light in accordance with sound vibrations which consists in applying an initial mechanical stress to a body that is isotropic in the unstressed condition, and birefringent when stressed, passing a beam of polarized light through said body, generating a high frequency electrical current, employing said current to apply a high frequency mechanical stress to said body, and modulating said current in accordance with said sound vibrations.

5. A method of controlling the intensity of a beam of polarized light in accordance with sound vibrations which consists in initially stressing in a body that is isotropic when unstressed and birefringent when stressed, passing a beam of polarized light through the point of maximum stress in said body, and applying to said body mechanical stresses varying in accordance with said sound vibrations.

6. Apparatus of the class described comprising polarizing means, a body that is isotropic when unstressed but birefringent when stressed, analyzing means, means for directing a beam of light through said polarizing means, body and analyzing means, means for applying an initial stress to said body, a stress applying member operatively connected with said body, and electro-magnetic operating means for said member.

7. Apparatus of the class described comprising polarizing means, a plurality of bodies that are isotropic when unstressed but birefringent when stressed, said bodies having substantial line contact with one another, analyzing means, means for directing a beam of light through said polarizing means, through said bodies through the line of contact therebetween, and through said analyzing means, means for forcing said bodies together to apply stress thereto, and electromagnetic operating means for said stress apply: ing means.

8. Apparatus of the class described comprising polarizing means, a plurality of bodies that are istoropic when unstressed but birefringent when stressed, said bodies having substantial line contact, analyzing means, means for directing a beam of light through said polarizing means, bodies, and analyzing means, said light beam passing through said line of contact, means for forcing said bodies together to apply an initial stress thereto, and. an additional stress applying member operatively connected to one of said bodies.

9. Apparatus of the class described comprising polarizing means, a plurality ofbodies that are isotropic when unstressed but birefringent when stressed, said bodies having substantial line contact, analyzing means, means for directing a beam of light through said polarizing means, bodies, and analyzing means, said light recting a beam of light through said polarizing means, at least one of said bodies, and said analyzing means, means for forcing said bodies together to apply an initial stress thereto, an additional stress applying member operatively connected to one of said bodies, and electro-magnetic operating means for said member.

11. Apparatus of-the class described comprising polarizing means, analyzing means, a plurality of bodies that are isotropic when unstressed but birefringent when stressed, means for directing a beam of light through said polarizing means, at least one of said bodies, and analyzing means, means for forcing said bodies together to apply an initial stress thereto, and an additional stress applying member operatively connected to one of said bodies.

ALFRED WHITAKER. 

